Sidney R. J. Smith (1858–1913) was a Late Victorian English architect, best known for the work he undertook in the 1880s and 1890s for the philanthropist Henry Tate including the original Tate Gallery at Millbank.
His works includes:
- Durning Library,
- Outdoor Relief Station, Norwood (1887)
- Tate Free Library, South Lambeth Road (1887)
- Durning Library, Kennington (1889)
- Tate Free Library, Streatham (1890)
- Tate Free Library, Brixton Oval (1892)
- Cripplegate Institute, 1 Golden Lane (1896)
- National Gallery of British Art (Tate Gallery) (1897)
- 16–19 Dunraven Street, Mayfair (1897)
- St Thomas, Telford Park, Streatham Hill (with Spencer William Grant)
- Tate Mausoleum, West Norwood Cemetery (c.1890)
- Euston Underground station, City and South London Railway (1907) (demolished)